Pool Chlorine Calculator
Calculate the exact chlorine dose for your pool — liquid bleach, cal-hypo, dichlor, trichlor, or lithium hypochlorite. Enter volume, current and target FC to get the result in fl oz, lbs, or kg.
Always test FC before adding and again after 30 minutes of circulation. Combined chlorine (CC) above 0.5 ppm means you need to shock, not just chlorinate. pH above 7.8 kills chlorine efficiency.
- Always test FC before adding and retest after 30 min of circulation.
- If combined chlorine (CC) is above 0.5 ppm, shock (raise FC to 10x CC) instead of just chlorinating.
- Chlorine efficiency drops sharply above pH 7.8. Lower pH to 7.2-7.6 first.
- Dichlor and trichlor add cyanuric acid (stabilizer). Track CYA monthly - over-stabilization requires drain and refill.
- Cal-hypo raises pH and calcium hardness. Liquid bleach is neutral for daily use.
Chlorine dosage quick-reference chart
Use this table to estimate the dose for a 1 ppm FC increase across common pool sizes. The calculator above uses the same formula — multiply each cell by (target − current) for your real dose.
| Pool volume | Liquid 12.5% (gal) | Cal-Hypo 65% (lbs) | Dichlor 56% (lbs) | Trichlor 90% (lbs) |
|---|---|---|---|---|
| 5,000 gal | 0.03 | 0.06 | 0.07 | 0.05 |
| 10,000 gal | 0.06 | 0.13 | 0.15 | 0.09 |
| 15,000 gal | 0.09 | 0.19 | 0.22 | 0.14 |
| 20,000 gal | 0.12 | 0.26 | 0.3 | 0.19 |
| 25,000 gal | 0.16 | 0.32 | 0.37 | 0.23 |
| 30,000 gal | 0.19 | 0.38 | 0.45 | 0.28 |
Values = dosage to raise FC by 1 ppm. Multiply by (target − current) for your actual increase, or switch the product in the calculator above to match what you actually buy.
What FC level should my pool be at?
Standard pool: aim for 1-3 ppm FC. Heavy use / hot weather: 3-5 ppm FC. Shock level: 10x CC (breakpoint chlorination) — only used to break out combined chlorine, not for daily maintenance. CYA level matters too — at 30 ppm CYA you want 3–5 ppm FC; at 50 ppm CYA you want 5–8 ppm FC to keep the same sanitizing power.
Which chlorine product should you choose?
Liquid bleach / sodium hypochlorite (8.25 / 10 / 12.5%)
The cleanest daily choice. No CYA, no calcium, no pH drift (FC neutral after the dose dissipates). More expensive per ppm than cal-hypo, but it does not push other parameters around.
Cal-hypo granular (65 / 73%)
Strong, fast, and inexpensive per ppm of FC. The trade-off: every dose raises pH and calcium hardness. Skip it on hard-water pools or test and adjust pH after every dose.
Dichlor (56%)
Stabilized chlorine in a fast-dissolving granular. Adds about 0.9 ppm CYA per 1 ppm FC — fine for occasional use, risky as a primary sanitizer on a long-running SWCG pool.
Trichlor tablets (90%)
The classic floating puck or in-line feeder tablet. Highest available chlorine and adds CYA at roughly 0.6 ppm per 1 ppm FC. Easy to over-stabilize within a season — track CYA monthly.
Lithium hypochlorite (35%)
Fast-dissolving granular. Does not add CYA or calcium and dissolves completely — ideal for hot tubs, small above-ground pools, and indoor pools where residue matters.
How to add chlorine
- Test FC, CC, pH, and CYA with a drop-count kit (Taylor K-2006 or TF-100).
- Adjust pH to 7.2–7.6 first if it is above 7.8.
- Compute the dose in the calculator above, picking your actual product.
- Liquid: pour slowly in front of a return jet with the pump running. Granular: pre-dissolve in a bucket of pool water if the label requires it.
- Run the pump for 30 minutes, then retest FC before anyone swims.
- If CC is above 0.5 ppm, switch to the Shock Calculator — adding chlorine alone will not fix it.
What is free chlorine (FC) vs combined chlorine (CC)?
Free chlorine (FC) is the active sanitizer doing the work. Combined chlorine (CC) is the spent chloramines that cause the classic "chlorine smell" and eye irritation. Total chlorine = FC + CC. If CC exceeds 0.5 ppm, you need to shock (raise FC to 10x CC) — not just add maintenance chlorine.
How much bleach to raise FC by 1 ppm in 10,000 gallons?
About 10.7 fl oz of 12.5% sodium hypochlorite, or 16.2 fl oz of 8.25% household bleach. The calculator above uses your exact pool volume and target — pick the product you actually have on hand.
Can I use cal-hypo for daily chlorination?
You can, but it raises both pH and calcium hardness on every dose. For most pools liquid bleach (10–12.5%) is the cleaner daily choice — no pH drift, no calcium creep. Reserve cal-hypo for shock treatments or when you specifically need to bump calcium.
Do dichlor and trichlor add stabilizer (CYA)?
Yes — every dose does. Dichlor adds ~0.9 ppm CYA per 1 ppm FC; trichlor adds ~0.6 ppm CYA per 1 ppm FC. If you use them as your primary sanitizer, your CYA climbs steadily through the season. Test monthly and plan partial drains before CYA crosses 100 ppm.
What if my pH is high (>7.8)?
Chlorine efficiency falls off a cliff above pH 7.8 — at pH 8.0 only about 20% of your free chlorine is in the active HOCl form. Drop pH to 7.2–7.6 first, then dose. Otherwise you will keep adding chlorine with almost no sanitizing payoff.
How often should I test and dose?
Test FC daily during swim season, more often in hot weather or after heavy use. Maintain 1–3 ppm FC for standard pools, 3–5 ppm for heavy use. Always retest 30 minutes after a dose. Use a drop-count kit (Taylor K-2006 or TF-100) — strips read inconsistently for FC/CC.